1. Field of the Invention
The invention relates to a plate valve.
2. Description of the Related Art
EP 0 631 0 56 has disclosed a plate valve for an actuator of a control valve. The plate valve has an upper opening in which there is oil. The upper opening, which is connected to a driving volume, leads in the centre of the valve to a plate which is mounted on a spring and which separates the driving volume from a spring space. The end of the upper opening forms a cylindrically formed sealing seat. The spring space below the plate is operatively connected to a proportional valve by an opening and a line. If the pressure in the spring space below the plate is lowered by means of the proportional valve, the plate drops due to the higher pressure of the oil in the upper opening above the plate. This frees the path for the oil, which can flow from the upper opening, past the plate, through openings which are distributed over the circumference, around the cylindrically formed sealing head. In this position, the plate valve is open. To prevent the oil from escaping laterally from the plate to the spring space, there is a sealing part between the rim of the plate and the housing. The plate valve is closed again by increasing the pressure below the plate by means of the proportional valve. The relative difference in pressure raises the plate again and thereby prevents the oil from flowing from the upper opening to the openings arranged around the circumference of the sealing seat. There is then a flow of oil from the spring space to the upper opening through orifice plates situated in the plate.
An important factor in the design of a plate valve is the sealing area ratio .lambda..sub.1 =A.sub.2 /A.sub.1, A.sub.2 being the lower area of action and A.sub.1 the upper area of action of the plate on which the pressure can act. It essentially determines the dynamic characteristics of a plate valve. A small sealing area ratio .lambda..sub.1 means that the valve has a better dynamic response but brings with it the disadvantage that it increases the diameter of the plate and hence of the entire valve. The plate valve described in EP 0 631 056 has this disadvantage. Particularly when designing a plate valve for an actuator of a control valve which must be closed very quickly in the event of an emergency shutdown of the plant, an actuator plate valve designed in this way has a very large diameter and, as a result, is very expensive to manufacture.